Remove white papery skin from garlic head (do not peel or separate the cloves). Wrap garlic head in foil. Bake at 350° for 45 minutes or until tender; cool 10 minutes. Separate cloves; squeeze to extract garlic pulp. Discard skins.
Heat a Dutch oven over medium-high heat. Coat pan with cooking spray. Add onion; sauté 10 minutes or until tender and golden brown. Add 4 garlic cloves; sauté 1 minute. Spoon onion mixture into a bowl.
Place flour in a shallow bowl or pie plate. Dredge lamb in flour, shaking off excess. Heat oil in pan over medium-high heat. Add half of lamb mixture; sprinkle with 1/4 teaspoon salt and 1/8 teaspoon pepper. Cook 6 minutes, browning on all sides. Add browned lamb to onion mixture. Repeat procedure with remaining lamb mixture, 1/4 teaspoon salt, and 1/8 teaspoon pepper.
Add wine to pan, scraping pan to loosen browned bits. Stir in lamb mixture and broth; bring to a boil. Cover, reduce heat, and simmer 1 hour or until lamb is just tender.
Stir in potatoes and parsnip. Cover and simmer 30 minutes. Stir in roasted garlic, remaining 1/2 teaspoon salt, remaining 1/4 teaspoon pepper, and rosemary; simmer 10 minutes.